Apparatus for measuring pressure



Feb. 20, 1951 S. CROMER ET AL APPARATUS FOR MEASURING PRESSURE Filed Oct. 11, 1945 2 Sheets-Sheet 1 INVENTOR EUGENE T. BOOTH JR. SYLVAN ORONER FRD 1.. ALEXANDER BY ATTORNEY Feb. 20, 1951 s. ,CROMER ETAL 2,542,905

APPARATUS FOR MEASURING PRESSURE Filed Oct. 11, 1945 2 Sheets-Sheet 2 1s 13 no INVENTOR EUGENE 1. BOOTH J R.

SYLVAN CROMER FRED L. ALEXANDER M firTORNEY Patented Feb. 20, 1951 APPARATUS FOR MEASURING PRESSURE Sylvan Cromer, Oak Ridge, 'lenn., and Eugene T. Booth, Jr., and Fred L. Alexander, New York, N. Y., assignors to the United States of America as represented by the United States Atomic Energy Commission Application October 11, 1945, Serial No. 621,865

4 Claims.

This invention relates to the measurement oi. pressure and more particularly to an improved apparatus for measuring the pressure of a corrosive fluid with a high degree of accuracy.

The measurement of the pressure of a corrosive fluid presents certain problems which are not encountered in measuring the pressures of non-corrosive fluids. Although numerous primary pressure measuring devices are known in the art, the number of these primary devices that may be used with corrosive fluids is limited by the fact that many of these devices operate in such manner that the chemical attack of the corrosive fluid tends to damage the device or render it inaccurate. Of the various known devices for measuring pressure, manometric measuring devices are in general the most accurate in cases where moderate pressures are to be measured. However such manometric devices cannot usually be employed directly in the case of corrosive fluids since the corrosive fluid is likely to react with the measuring fluid of the manometer. It is thus necessary to provide some means of preventing contact between the corrosive fluid and the measuring fluid of the manometer. So far as is known all of the prior methods for preventing contact between the corrosive fluid and the manometer fluid result in a decrease in accuracy and/or sensitivity of the measuring device.

It is accordingly an object of the present invention to provide an improved device for manometrically measuring the pressure 01' a corrosive fluid such as, for example, a fluid containing fluorine or a fluorine-containing compound.

It is another object of the invention to provide a pressure measuring device for measuring the pressure of a corrosive gas with an unusually high degree of accuracy.

It is still another object of the invention to provide a pressure measuring device capable of indicating the pressure of a fluid independent of barometric pressure.

Other objects of the invention will be in part obvious and in part pointed out hereinafter.

The principle of operation of the present invention comprises in general measuring the pressure of a corrosive fluid by establishing an inert fluid pressure that counteracts the corrosive fluid pressure, maintaining the inert fluid pressure at a value suflicient to balance the corrosive fluid pressure and measuring the inert fluid pressure as a measure of the corrosive fluid pressure. Apparatus in two alternative embodiments of the present invention is shown in the accompanying drawings.

advantages of the present apparatus may be best The many objects and appreciated and understood by reference to the drawings wherein Fig. 1 is an axial cross-sectional view of a differential pressure responsive device;

Fig. 2 is a diagrammatic view of apparatus incorporating the differential pressure responsive device of Fig. 1 in such manner as to measure the pressure of a corrosive fluid in the pressure range below atmospheric pressure;

Fig. 3 is a diagrammatic view of apparatus similar to that of Fig. 2 but arranged to operate at a pressure either above or below atmospheric pressure.

Referring to the drawings and particularly to Fig. 1 the numeral I0 designates a relatively thin flexible diaphragm constructed of a corrosion resistant material such as, for example nickel, and sealed between two slightly cupped discs i2 and H in such manner that the discs I2 and I4 cooperate to define an enclosed space which is divided into two chambers l3 and I5 by the diaphragm ill. The discs I2 and I4 are also preferably made of nickel and they and the diaphragm III are sealed at their peripheries by an atomic hydrogen weld It. The nickel discs I 2 and H are flxed to a pair of supporting discs l8 and 20 in any suitable manner such as by soldering, the function of the supporting discs l8 and 20 being to strengthen and support the nickel discs i2 and I4. Further support for the structure thus far described is provided by a pair of peripheral rings 22 and 24 which are provided with the internal annular steps or shoulders 25 and 28 respectively that fit over the peripheral portion of the discs l8 and 20. The rings 22 and 24 are pressed together in any suitable manner such as Y by the bolts 30 to insure that the diaphragm I 0 is held firmly between the nickel discs [2 and i4 and to assist and reinforce the atomic hydrogen weld IS in maintaining a tight joint at the periphery of the discs l2 and H.

The chamber I5 is connected by a conduit 32 with a corrosive fluid system (not shown) in which the pressure is to be measured. For example the present device has been used to measure the pressure in a system containing uranium hexafluoride vapor under a pressure of about two pounds per square inch absolute. Since the walls of chamber 15 are constructed entirely of a corrosion resistant material there will be little if any chemical attack on these parts by the fluoride vapor. The diaphragm i0 is sufliciently thin to be deflected by the pressure exerted by the fluid in chamber I8 and in accordance with the present invention an inert fluid is introduced into the chamber I3 to establish a pressure that is just sufficient to balance the pressure in the chamber I8. This balancing pressure is measured as a measure of the corrosive fluid pressure. Inert pressure fluid is introduced into the chamber I3 through the conduit 34 in a manner described in detail hereinafter.

The nickel disc I2 and supporting disc I8 have a central hole into which an annular flange 38 of an annular plate 38 extends. The plate 88 is fixed to the supporting disc I8 in any suitable manner such as by the screws 48. The diaphragm I8 is provided with a button 42 that acts as an electrical contact and cooperates with a second electrical contact 44 supported in a block 48 that is mounted on the plate 38 by means of the screws 48. The screws 48 pass through the holes 88 in the block 48, the diameter of the holes 58 being suiilciently greater in diameter than the screws 48 to prevent electrical contact between the screws and the block 48. Th4. screws 48 are further electrically insulated from the block 46 by the outer insulating discs 82, the insulating sleeves 58, and inner insulating discs 54, the inner discs 54 being effectively interposed between the block 48 and the plate 38 to insulate the block from the plate. The contact 44 is made adjustable with respect to the contact 42 by being mounted on a threaded shaft or adjusting member 58 that passes through the center of block 48. In order to prevent escape of pressure fluid from chamber I3 around the adjusting member 58 a packing 58 is provided that is held in place by a bushing or packing nut 88 which is threaded into the block 48. The construction is such that the adjusting member 58 may be rotated to so position the contact 44 that an electrical circuit will be completed through the contact 44 and button 42 on diaphragm I8 when the diaphragm is defiected by an increase in pressure in chamber I8 relative to the pressure in chamber I3. Thus the device shown in Fig. 1 is adapted to cooperate with a source of electrical energy to establish an electrical signal when the pressure in chamber I exceeds the pressure in chamber I3 and this electrical signal may be used to regulate the flow of pressure fluid through conduit 34 into chamber I3 in such manner as to rebalance the pres sures in chambers I3 and I5.

The rebalancing of the pressures in chambers I3 and I5 may be effected in various ways and two ways of maintaining such a pressure balance are shown in Figs. 2 and 3. Referring first to Fig. 2 the adjusting member 58 and contact 44 are connected through a resistance 82 with the grid 84 of an electronic tube 88 of well-known construction. Electrical energy is supplied through the leads 68 from a suitable source of 110 volt alternating current to the filament "I8 and plate 12 as well as to the grid 84 of the tube 88. The plate circuit includes a coil I4 of a relay generally designated as I8 and also includes a condenser I8. The grid circuit includes a resistance 88 in addition to the resistance 82. The filament circuit includes a resistance 8 I. The resistances 82, 88 and 8I may, for example, have values of one megohm, 150,000 ohms and 250 ohms, respectively.

The relay I8 regulates the supply of pressure fiuid to the chamber I3 of the differential pressure responsive device. In addition to coil 14 the relay I8 includes an armature 82 which is pivoted at 84 and normally urged by a spring 88 downwardly against a small nozzle 88. The armature 82 is provided with a valve member 88 which is adapted to bear against the end of nozzle 88. The armature 82 and valve member 88 comprise a flapper valve that cooperates with the nozzle 88 to regulate the flow of fluid, in this case air, entering the nozzle 88. Nozzle 88 is connected to the pipe 34 which leads to the chamber I3 and also to the vacuum pipe 82 which leads to a suitable vacuum pump (not shown). The pipe 82 is provided with a regulating valve 84 that may be manually adjusted to regulate the rate at which the chamber I3 and pipe 34 are evacuated. Also connected to the nozzle 88 and pipe 34 there is an absolute pressure manometer 88 containing a suitable measuring fluid such as the oil 88. The end I88 of the manometer 88 is sealed in well-known manner so that the diilerence in level of the oil 88 in the two arms of the manometer 88 indicates the absolute pressure within the pipe 34 and chamber I3. A suitable scale I82 is provided for reading this differential level. If desired a conventional recording pressure instrument I84 may be connected into the pressure system by a pipe I88. However it highly accurate results are desired the reading of the manometer 88 should be relied upon since the manometer is much more sensitive to small variations in pressure than is a conventional pressure recorder.

The operation of the apparatus shown in Fig. 2 is largely apparent from its description. The valve 84 in vacuum pipe 82 is initially adjusted in such manner that the pressure system including chamber I3, pipe 34, nozzle 88 and manometer 88 is continuously evacuated at a relatively slow rate. In the illustrative case here being described the chamber I8 communicates through pipe 32 with a system containing uranium hexafluoride vapor under a pressure of about 2 p. s. i. absolute and the apparatus of Fig. 2 operates to maintain the pressure in chamber I3 equal to the pressure in chamber I8. If, for example, the pressure in chamber I5 exceeds the pressure in chamber I3 the diaphragm I8 will be deflected to the right as shown in Fig. 2 to cause the button 42 to bear against contact 44 and an electrical circuit is completed through the button and contact. Current will flow through resistance 82 thus decreasing the negative bias of grid 84 and producing an increase in the plate current of the tube 88. The increased current in the plate circuit flows through the coil I4 of relay l8 and the relay is so adjusted that this increase in current is sufiicient to actuate the relay to cause the armature 82 to be drawn upwardly against the tension of spring 88. The condenser I8 in the plate circuit performs its well-known function of smoothing out the irregularities in the pulsating direct current that flows in the plate circuit.

When armature 82 is moved upwardly toward coil 14 valve member 88 is withdrawn from the end of nozzle 88 and air flows inwardly through nozzle 88 and pipe 34 to the chamber I3 of the differential pressure responsive device. The relationship between the adjustment of valve 84 and the size of the opening oi the nozzle 88 is such that during the period the valve member 88 is away from the nozzle 88 the pressure will build up in the chamber I3.

When the pressure in chamber I3 exceeds the pressure in chamber I5 the diaphragm I8 is deflected toward the left as shown in Fig. 2 and the circuit through button 42 and contact 44 is broken. The operations described above occur in a reverse sense and relay I6 is partially deenergized to permit spring 86 to draw armature 82 downwardly. Valve member 90 is drawn against the end of nozzle 88 and the pressure in the chamber I3 starts decreasing again due to continued withdrawal of air from the system through pipe 92.

The net result of the above operations is that the pressure in chamber I3 is maintained substantially equal to the pressure in chamber I5 within very close limits. The operation of the electronic tube 66 is, of course, very rapid and the inertia of the armature 82 and valve member 90 are very small. The clearance between the button 42 and contact 44 may be made of the order of .001 inch. Therefore the operations described above can occur very rapidly and thus there is no substantial deviation of the pressure in chamber I3 from the pressure existing in chamber I5. As pointed out above the resistance 62 is made relatively large, preferably of the order of one megohm, to reduce the current flow through the electrical contacts to a relatively low value and thereby prevent damage to the contacts because of sparking. The manometer 96 responds accurately and sensitively to the pressure in pipe 34 and chamber I3 and therefore the reading of the manometer may be taken as a measure of the corrosive gas pressure in chamber I5. A relatively rough record of the pressure may be obtained by using the pressure recorder I04.

An alternative apparatus adapted to measure pressures either above or below atmospheric pressure is shown in Fig. 3. The apparatus of Fig. 3 is generally similar to that of Fig. 2 and only the differences between the two systems need be described. In Fig. 3 the coil I4 and armature 82 of relay 16 are encased in a closed chamber I08 that communicates through a pipe I09 and pipe 34 with chamber I3. Inserted in the chamber I08 there are two opposed nozzles H and II 2, the nozzle IIO being connected to a source of air under pressure and the nozzle II2 being connected to a vacuum pump (not shown). The valve member 90 of the armature 82 is adapted to be drawn against one or the other of the nozzles I I0 and 2 by the spring 86 or relay coil I4 respectively.

The operation of the apparatus shown in Fig. I

3 is as follows: When the pressure in chamber I exceeds that in chamber I3 the button 42 is forced against the contact 44 and the current flow through coil I4 of relay 16 increases as previously described. Valve member 90 is drawn downwardl to close off vacuum nozzle II 2 and open air nozzle IIO to cause the pressure in chamber I08, pipe 34 and chamber I3 to increase. On the other hand when the pressure in chamber I3 exceeds the pressure in chamber I 5 armature 82 is drawn upwardly by the spring 86 and valve member 90 closes air nozzle I I0 and opens vacuum nozzle I I2 to cause the pressure in chamber I3 to decrease. As in the case of the apparatus of Fig. 2 the pressure in chambers I3 and I5 will be maintained substantially equal and the inert gas pressure in chamber I3 may be measured by the manometer 96.

It has been found that the apparatus of the present invention permits the measurement of the pressure of a corrosive gas with exceptional accuracy. In some cases, for example, the pressures of corrosive gases have been measured with an accuracy of better than 0.1% even at pressures as low as 2 p. s. i. absolute. By utilizing the absolute pressure manometer 96 the measurement may be made Wholly independent of barometric pressure and thus any errors that might arise from an independent measurement of barometric pressure and suitable correction for barometric pressure are eliminated. Although the present apparatus is particularly useful for measuring the pressures of corrosive fluids it may, of course, be used to measure the pressures of non-corrosive fluids as well. Either the measured fluid or the controlled fluid may be either a liquid or a gas.

It is evident that the present apparatus ma be used to measure differential pressure as well as a single pressure. In measuring differential pressure two dillerential pressure responsive devices and their associated pneumato-electrical systems as shown in Figs. 2 and 3 are connected to opposite arms of a manometer such as the manometer 96. The manometer indicates the differential pressure. When used for measuring differential pressure the present apparatus is exceptionally accurate. In some cases difierential pressure measurements have been made with an accuracy of better than 0.01%.

It is to be understood that the foregoing description is intended to be illustrative only and other applications of the present apparatus as well as modifications thereof within the scope of the invention will be apparent to those skilled in the art.

We claim:

1. In apparatus for measuring the pressure of a fluid, in combination, a flexible diaphragm having one side exposed to the pressure to be measured, said diaphragm being deflectable by said measured pressure, fluid pressure supply means for supplying a controlled fluid pressure to the other side of said diaphragm, means cooperat ing with said diaphragm for establishing an electrical signal when said diaphragm is deflected by said measured pressure, valve means for regulating the fluid pressure supplied by said fluid pressure supply means, said valve means comprising a nozzle and cooperating flapper valve, means responsive to said electrical signal for adjusting said flapper valve to maintain said controlled pressure substantially equal to said measured pressure, and means responsive to the magnitude of said controlled pressure for indicating the magnitude of said measured pressure.

2. In apparatus for measuring the pressure of a fluid, in combination, a flexible member having one side exposed to the pressure to be measured, said member being deflectable by said measured pressure, a source of fluid under pressure, a fluid pressure system for conducting pressure fluid from said source to the other side of said member, said system comprising regulating means for maintaining a relatively small regulated flow into said system, a nozzle permitting escape of fluid from said system and a flapper valve for controlling the escape of fluid from said system to control the pressure in said system, means cooperating with said member for establishing an electrical signal when said member is deflected by said measured pressure, means responsive to said electrical signal for adjusting said flapper valve to maintain the pressure in said system substan tially equal to said measured pressure, and means responsive to the magnitude of said controlled pressure for indicating the magnitude of said measured pressure.

3. In apparatus for measuring the pressure of a fluid, in combination, a flexible member having one side exposed to the pressure to be measured, said member being deflectable by said measured pressure, a source of fluid under pressure, a fluid pressure system for conducting pressure fluid from said source to the other side of said member, said system comprising a first nozzle regulating admission of pressure fluid to said system, a second nozzle regulating escape of said fluid from said system and a flapper valve cooperable with said two nozzles to selectively close one of said nozzles and open the other of said nozzles to control the pressure in said system, means cooperating with said member for establishing an electrical signal when said member is deflected by said measured pressure, means responsive to said electrical signal for adjusting said flapper valve to maintain the pressure in said system substantially equal to said measured pressure, and means responsive to the magnitude of said controlled pressure for indicating the magnitude of said measured pressure. I

4. Control apparatus for establishing in a fluid pressure system a fluid pressure substantially equal to a variable pressure comprising, in combination with said fluid pressure system, a source of fluid under pressure for supplying pressure fluid to said system, regulating means for regulating the flow of pressure fluid to said system, said regulating means comprising a nozzle permitting escape of said fluid from said system and a cooperating flapper valve, means responsive to said variable pressure and to said fluid pressure for creating an electrical signal when said variable pressure departs from said fluid pressure, amplifying means for amplifying said electrical signal, and means responsive to said amplifled signal for adjusting said flapper valve to maintain said fluid pressure substantiall equal to said variable pressure.

SYLVAN CROMER.

EUGENE T. BOOTH, Ju.

FRED L. ALEXANDER.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS 

